Top end is about 2200F and that is for a few types of air-cooled tool steel; however some of the A-type steels are down in the 1800F range. More commonly, 1500 to 1650F is needed for low, medium and high carbon steels and alloys. Most of my work is done at 1550 and 1575F. BTW, these are austentizing temperatures, not melting temperatures.
In addition to a decent heat treat oven, you need either a visual spectrometer or high-end IR thermometer. For accurate/critical treating you cannot just look at the color or use a magnet to determine proper phase changes. You also need some method of oxygen deprivation. I've had good luck using a small burn-off piece along with argon gas flooding. Stainless steel foil is very expensive and error prone (not to mention, sharp as a razor and hard to handle). And of course, proper safety equipment.
Be apprised that at these temperatures, you are not playing games. The kinds of burns you get from this cause primal screams and foaming at the mouth and nostrils -long before you get the first cuss-words out of your mouth...
As far as casting (which I have no experience) I tend to think these temps are best for aluminum and other metals in the temperature range mentioned above. The ovens I'm referring to are heated with nicrome or kanthal wire. Nicrome tops out with a usable temperature of about 2000F and kanthal will go up to 2200F (usable oven temp). Beyond that, you need to get into carbon arc and there's not enough electricity in your service panel to get to high volume melting of around 2600F for steel forging.
Here's a reference chart of melting temperatures:
http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html
PS: I have a sizeable thread here about a shop made heat treating furnace and I do a good bit of it with good results.
Ray
What's the top end required for a heat treat furnace? Can you use the same furnace to heat a crucible for casting or is that not recommended?
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